This invention relates to a roller guide arrangement for the canvas or dry felt belts in a multicylinder type dryer section of a paper machine.
Generally, in a conventional arrangement, a freshly formed paper sheet is passed sequentially between one or more endless belts of canvas or felt, and cylindrical dryers. The belts and dryers are combined into a plurality of groups so that the paper can pass from cylinder to cylinder and the belts can be separated for their own drying and cleaning.
FIGS. 1 and 2 show schematically a multi grouped-multi-cylinder dryer system of conventional arrangement in paper making machines. The cylinders 1, 1a . . . 1e are grouped into four groups, namely an upper front group G.sub.1, a bottom front group G.sub.2, upper rear group G.sub.3 and a bottom rear group G.sub.4. The groups are provided with an endless, continuously moving drying belt of canvas or felt, 4, 5, 6 and 7 respectively, which are driven and directed by rollers 2, 2.sub.1 . . . 2.sub.n. A freshly formed paper sheet is passed into the bottom preceding groups G.sub.1 between the belt 4 and the cylinder 1, and passes from cylinder to cylinder, being carried by the entrained succession of belts. Generally, the separated runs, or return runs of the bottom belts 4 and 7, being spaced from each other, form a chimney effect through which space an air draft X from below eg: basement, enters.
In either figure, if the upward air current or draft X from the basement below is excessively large in a zone A, flapping will occur in zones C and D, through which only the paper sheet passes, indicated by chain lines, causing trouble during high speed operation.
To minimize the draft X, therefore, a seal zone B usually is formed by the roller 2 and the belts 4, 7. FIG. 1 illustrates a point seal established by the roller 2 and the belt 7 at one point (actually the seal is linear because the arrangement has a depth at right angles to the plane of the drawing, the same applying hereinafter). FIG. 2 illustrates a linear seal formed by the belts 4 and 7 (actually the seal is planar for the reason explained above, the same applying hereinafter).
In either case, the seal zone B constitutes a major obstacle in the path of the broke that will result from a break in the sheet passing around the particular dryer, which will be dropped off and accumulate in the zone A. The broke cannot fall through the seal zone, thus unfavorably affecting the operational efficiency.
The present invention has as its object the elimination of the foregoing obstacle. The invention contemplates the provision of a roller arrangement which can strikingly enhance the operational efficiency, while maintaining about the same degree of sealability as by the conventional arrangements. This is effected by the introduction of a seal roll into the space or chimney between return run sections of the felts.